The Helsinki festival's second announcement also includes the Canadian indie star Mac DeMarco.
Joining Bon Iver, the sole act confirmed before today, will be UK grime giant Stormzy, US group Chromatics and FKA twigs, whose 2019 album, MAGDALENE, claimed the #1 spot in our end-of-year polls.
Other highlights include London singer-songwriter Michael Kiwanuka, Canadian indie star Mac DeMarco, punk artist Bikini Kill, UK R&B talent Mabel and reggae singer Koffee. Three Finnish acts have also been added: Henrik!, Teksti-TV 666 and popular rapper Gettomasa.
Watch our 360-degree film about Flow from 2017.